Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge.
SAG and ball mills are known types of grinding mills that are used to grind ores to smaller sizes. The mill typically comprises a main grinding body in the form of a rotating cylinder which is partially filled with balls, usually stone or metal, which grinds material to the necessary fineness by friction and impact with the tumbling balls. The cylinder has an entry inlet at one end and a discharge outlet at the other end. Material to be ground (e.g. ore) passes through the entry inlet of the cylinder and ground material passes out of the other end through the discharge outlet.
A feed chute is provided to convey the “raw” material into the entry of the main grinding body. The feed chute is also known as a mill chute or a conveyor chute, and sometimes simply as a chute. The feed chute typically comprises a trolley assembly on which an open top box like arrangement is supported. The box has an elongate outlet extending from a side wall. The feed chute can be rolled to the main grinding body of the mill such that the elongate outlet is pushed into the entry. Material to be ground can be dumped into the open box and will pass along the elongate outlet into the main grinding body. The elongate outlet can contain some form of outwardly extending protective surround flange which locates against or close to the walls surrounding the inlet of the grinding body to prevent material falling back out of the inlet.
SAG and Ball mills are commonly used in the grinding stages of mineral processing. During the grinding process, a large amount of heat is released.
It is a requirement to periodically inspect the inside of the mill for wear and tear to the liner, the balls or other parts and components inside the mill. The mill must be shut down and isolated prior to internal inspection.
A common technique is to retract the feed chute and have workers enter into the cylinder to inspect the components. Additional isolation processes are required for the removal and re-insertion of the feed chute. It is also a physically involved activity and the whole process often takes several hours due to the work required as well as the safety procedures that must be implemented.
Any time the feed chute is retracted there are potential safety risks. A grinding mill is a confined space which also brings safety risks. These risks are increased within a grinding mill due to the unstable environment. The surface is wet and uneven, making it difficult to walk on. As the mill cools, the grinding media (steel balls) can explode. Rocks and balls can become stuck in the liners around the mill and these can dislodge and fall on personnel entering the mill.
It is known to provide observation holes in the feed chute area through which observations can be made. These holes are covered over with steel plates when the mill is in operation and are only opened when the mill is shut down and isolated. This is a time consuming process and only allows limited viewing ability. Additionally, the area around the mill can be quite hazardous to operators and it is therefore not considered desirable to have an operator in close proximity to the mill for the purposes of viewing.
The cost of such downtime is often hundreds of thousands of dollars of lost production.
Another disadvantage with existing inspection techniques is that real time observations cannot be made while the mill is in operation to immediately observe any potentially adverse conditions. One reason for this is the extremely hostile conditions inside the mill. Real time observations may increase grinding efficiency, allow for improved liner design, provide information to adjust the mill rotation speed, ore feed rates, and mill ball feed rates among others.
The interior of the mill, as mentioned above, comprises extremely hostile conditions and any monitoring device merely placed inside the mill will almost certainly be pulverised or damaged beyond repair.
It is considered that a visual observation of the interior of the mill can provide the most important source of data and therefore visual data of the interior of the mill during use is considered to be highly valuable providing that the visual date can be secured reliably and without constant replacement of the monitoring device in the mill.
There would be an advantage if it were possible to monitor the inside a mill while it is in operation. There would be a particular advantage if it were possible to visually monitor the inside of the mill during operation.
It is an object of the present invention to provide a method and apparatus that can monitor the inside of a mill while it is in operation.